Crank assembly for a full-suspension bicycle

ABSTRACT

A crank assembly for a bicycle uses a chain and a plurality of auxiliary sprockets to achieve high ratios of wheel speed to pedal-rotation speed. The crank assembly is designed for use on a full-suspension bicycle, as the relative motion of the drive sprockets ( 22 ) of the transmission is isolated from the motion of the rear suspension arms ( 18, 20 ), which form the chain stays of the bicycle, and whose pivot is co-axial with the axle of the pedal cranks ( 14 ). Motion of the suspension arms about the pivot induces rotation by an equal angular measure of the drive sprocket of the transmission. So no relative motion of the drive sprocket and suspension arms occurs except that which is induced by the pedal cranks.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] (not applicable)

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0002] (not applicable)

BACKGROUND—FIELD OF INVENTION

[0003] The invention relates to the drivetrains for full-suspensionbicycles.

BACKGROUND—DESCRIPTION OF PRIOR ART

[0004] The use of different-sized sprockets between the pedals and thedrive wheel of a bicycle to increase the speed of the bicycle has beenwell-known for many years in the prior art. In the use of rearsuspension for the bicycle, many attempts have been made in the priorart to isolate the transmission from the motion of the suspension arm,thus eliminating unwanted pedal-induced motion of the suspension.

[0005] Many of the attempts made in the prior art depend on a particularrelative angular position of the rear-suspension arm and the rest of thebicycle frame. Thus when this position varies in the course of normaluse, the effectiveness of the mechanism in achieving the desiredobjective is compromised.

[0006] U.S. Pat. Nos. 5,205,572 and 5,226,674 to Buell, et al. (1993),and 5,217,241 to Girvin (1993) are examples of the most basicconfiguration for a bicycle rear suspension, that of a “swingarm”attached to the main frame by a pivot and providing a circulartrajectory of the rear axle relative to the main frame. Usually anattempt is made to minimize the influence of the drivetrain upon thesuspension by placing the pivot along or close to the line (when viewedfrom the side) of the part of the chain under tension. Again such aconfiguration is susceptible to the changing of the chain position dueto the shifting of the chain between sprockets. Such a problem ispresent also with the double spring assembly design described in U.S.Pat. No. 6,131,934 to Sinclair (2000).

[0007] Attempts have been made to reduce this effect by creating anon-circular trajectory for the rear wheel relative to the main frame.This trajectory is usually created by means of a four-bar linkage. U.S.Pat. Nos. 4,789,174 (1987) and 5,121,937 (1992) to Lawwill show rearsuspension configured in a trapezoidal arrangement, which creates atrajectory of the rear wheel relative to the main frame so as to reducethe action of the pedaling force and resultant chain tension upon thesuspension. However, when the chain is shifted between the drive andrear sprockets, the varying position and angle of the part of the chainunder tension, makes the influence of the tension upon the suspensionunavoidable. Four-bar linkages are also described in U.S. Pat. Nos.5,306,036 (1994), 5,409,249 (1995), and 5,441,292 (1995) to Busby,5,678,837 (1997) to Leitner, and 6,102,421 to Lawwill, et al. (2000).

[0008] A different way of achieving a non-circular trajectory of therear wheel is also described in U.S. Pat. Nos. 5,509,679 (1996) and5,899,480 (1999) to Leitner. Here the trajectory is created by makingthe shock absorber itself a structural part of one of the members of thelinkage. This design has the same disadvantages, described above, asdoes the four-bar linkage.

[0009] A different attempt to isolate the drivetrain from the suspensionhas been made by placing the entire drivetrain on the pivotingchainstay. This eliminates the influence of the drivetrain upon thesuspension, as the relative position of the drive sprockets and rearsprockets is fixed. Such a configuration is described in U.S. Pat. Nos.5,474,318 to Castellano (1995), 5,685,553 to Wilcox, et al. (1997), and6,109,636 to Klein (2000). However, such a configuration makes thestiffness of the suspension when the rider is seated different from thatwhen the rider is standing. Such variation in stiffness is actually theaim of some suspension designs, such as U.S. Pat. No. 5,611,557 toFarris, et al. (1997). Such a design uses this variation to reduce theenergy lost due to the “bobbing” which occurs when the rider is standingand pedaling hard. Again, such a solution is reached at the cost ofincreased stiffness while standing, which causes fatigue in the rider.

[0010] Other inventions involve an eccentric crank mechanism. Thiscauses compression of the suspension to effectively lengthen thechainstay to counterbalance the pedaling force of the rider. This isdescribed in U.S. Pat. Nos. 5,553,881 (1996) and 5,628,524 (1997) toKlassen, et al., and 6,099,010 to Busby (2000). This configurationsuffers from the fact that the pedaling force to be balanced varies,because of the changing terrain, because of the natural variation inapplied force during the pedal stroke, and because the effective forceexerted by the drivetrain upon the suspension varies with the shiftingof the chain between sprockets.

[0011] Another patent, U.S. Pat. No. 5,725,227 to Mayer (1998)—describesa configuration whereby the seat is mounted on an intermediate framemember, between the front portion which includes the steering tube, andthe rear portion which includes the drop-outs holding the rear wheel.Such a configuration does not eliminate the problem of variable chainposition present with the basic swingarm design.

[0012] Some designs make the pivot of the swingarm coaxial with that ofthe pedal cranks, as does the present invention. This is seen in U.S.Pat. No. 6,149,175 to Fujii (2000). But without the means, as in thepresent invention, whereby the motion of the swingarm induces likemotion of the drive sprocket, this is essentially the same configurationas that where the entire drivetrain is mounted on the swingarm. The samefixed chain length is created, but so is the same variation ofstiffness.

SUMMARY

[0013] In accordance with the present invention a crank assemblycomprises a plurality of gears for operating the drivetrain of abicycle, centered at and near the axis of the pedal cranks, and theproximal portions of the chainstays, which are free to rotate about thesame axis.

OBJECT AND ADVANTAGES

[0014] The object of the present invention is to eliminate the influenceof the drivetrain upon the suspension. Though the device involves moregears in the transmission of power than does the usual drivetrain, theefficiency will be at least as good as that of the internal multi-speedrear hub. An additional advantage of the device is that smallerchainrings are required, which increases the clearance between the largechainring and the ground. The increase in clearance and the isolation ofthe suspension from the drivetrain allow for rear suspension which bothhas long travel and is power-efficient. As well, the smaller chainringsdecrease the difference in radius between adjacent chainrings, allowingeasier operation of the front derailleur.

DRAWING FIGURES

[0015]FIGS. 1 and 2 depict an embodiment of a crank assembly,constructed according to claim 1.

[0016]FIG. 1 is a view of a crank assembly from the left-hand side.

[0017]FIG. 2 is a view of a crank assembly from the right-hand side.

[0018] Reference Numerals in Drawings

[0019]6, 6A: annular gears

[0020]8, 8A: gears

[0021]10, 10A: gears

[0022]12, 12A: links

[0023]14: axle of pedal cranks, coupled to these cranks

[0024]16: cylindrical axle, coupled to gears 10 and 10A

[0025]18: left-hand side chainstay

[0026]20: right-hand side chainstay

[0027]22: chainring, coupled to annular gear 6

DESCRIPTION—FIGS. 1 and 2—An Embodiment According to claim 1

[0028] The means of drivetrain-suspension isolation disclosed hereindepends on having

[0029] (i) A fixed distance between drive sprocket and rear axle tomaintain a constant chain tension.

[0030] (ii) A drive sprocket whose rotation relative to that of therear-suspension arm, about their co-axial pivots, is independent of therotation of the front (the rest of the 135 frame, the fork, the frontwheel, etc.) of the bicycle. Denote by “main axis” the common axis ofrotation of the pedal cranks, drive sprocket, and rear-suspension arm.Precisely, denoting by W_(crank), W_(drive), and W_(arm), the respectiveangular velocities about the main axis, with respect to the frame (themain triangle thereof), of the pedal cranks, the drive sprocket, and therear-suspension arm, which three have co-axial rotation, the inventionachieves a relation of

W _(crank) +W _(arm) =W _(drive)

[0031] among the variables. Thus,

W _(drive) −W _(arm) =W _(crank),

[0032] so that the motion (W_(drive)−W_(arm)) of the transmissionrelative to the rear-suspension 145 arm depends only on the motion ofthe pedal crank and not on the position of the suspension arm itself.

[0033] This relationship between W_(crank), W_(drive), and W_(arm) isachieved using a plurality of gears in the crank mechanism.

[0034]FIG. 1 depicts an embodiment of that described in claim 1, viewedfrom the left side of the bicycle. FIG. 2 depicts part of the sameembodiment, viewed from the right side of the bicycle so that parts 6,8, 10, and 12 are visible. The gears 6, 8, 10, 6A, 8A, and 10A haveteeth on their surfaces of contact, which teeth have been omitted fromthe figures for simplicity. As the chainstays do not rotate completelyaround the main axis, only a sector of the annular gear 6A need beembodied. This is seen in FIG. 2 welded to the left-hand side chainstay.

[0035] A novel feature of the present invention is the involvement ofthe motion of the rear-suspension arm, via the movement of gears, inthat of the transmission itself. Attempts made in the prior art toachieve the same end as achieved by the present invention generallyinvolve separate suspension system and transmission.

[0036] Advantages

[0037] The transferal of torque from the rider to the rear axle passesthrough only two points of engagement of gears in addition to the pointsof engagement of the usual sprockets, chain, and derailleur of the modemmulti-speed bicycle. This will provide an efficiency of torque transferat least comparable to that of the multi-speed rear hub. As well, theisolation of the pedal torque from the motion of the rear-suspension armis well-suited to the periodic nature of the torque applied by thecyclist to the drivetrain.

[0038] Whereas most rear-suspension systems provide from two to fiveinches of rear-wheel travel, the present invention would allow for ameasure of travel unhampered be the changing position of the suspensionarm, and restricted only by the geometry of the rest of the bicycle(such as the position of the seat), allowing for more travel than isfound in most suspension systems.

[0039] The increased ratio of rotation of pedal cranks to front (drive)sprockets (rather than the usual 1:1) means that the front (drive)sprockets are made smaller than is customary, increasing the ease ofoperation of the front derailleur and increasing the clearance from theground of the front sprockets and chain.

[0040] The present invention is especially suited to the multiple drivesprockets of the modern mountain bike. Attempts have been made in theprior art to isolate the drivetrain from the rear suspension by placingthe suspension-arm pivot axis so that it passes through the point ofinitial contact (near the top) of the drive sprocket with the chain,thus reducing to zero the torque of the chain upon the suspension arm.However, this has limited success when the point of initial contactchanges as the front derailleur shifts the chain between drivesprockets.

[0041] Operation

[0042] The rider applies force to the pedals, and thus torque to thepedal cranks about the main axis. This causes rotation of the link 12about the main axis, and thus rotation in the same direction of the gear8, both about its own pivot at one end of link 12, and about the mainaxis. The annular gear 6 is then caused to rotate in that direction. Itis linked to the drive sprocket, which powers the drivetrain of thebicycle.

[0043] The uneven surface of the ground causes the rear-suspension armto rotate about the main axis, which arm is linked to the annular gear6A. Through the engagement of 6A with 8A, 8A with 10A, the linking of10A and 10, the engagement of 10 with 8, and of 8 with 6, the drivesprocket is caused to rotate about the main axis, with an angularvelocity equal to that of the suspension arm. Thus the motion of therear suspension causes no relative motion of the drive sprocket andsuspension arm.

[0044] Conclusion, Ramifications, and Scope

[0045] Accordingly, this invention eliminates the influence of thedrivetrain of a bicycle upon the rear suspension. Additional advantagesof the device are provided by the smaller chainrings required. Theclearance between the large chainring and the ground is increased, andthe difference in radius between adjacent chainrings is decreased,allowing easier operation of the front derailleur.

[0046] While it is apparent that the invention herein disclosed iswell-calculated to fulfill the objects stated above, it will beappreciated that numerous modifications and embodiments may be derivedby those skilled in the art. It is intended that the appended claimscover all such modifications and embodiment as fall within the truespirit and scope of the present invention.

I claim:
 1. A bicycle having a frame, at least a rear wheel coupled tothe frame via a movable rear-suspension arm, and a drive and suspensionsystem including: a main sprocket, linked by a chain to a sprocketcoupled to the rear axle, rotating about the axis of rotation of themain sprocket (hereafter called the “main axis”), an annular gear 6whose teeth point inward toward the main axis, a gear 10 rotating aboutthe main axis, a link 12 pivoting at one end about the main axis, a gear8 rotating about another pivot attached to link 12 at its other end, amovable suspension arm pivoting about the main axis.
 2. The bicycle ofclaim 1, further including annular gear 6A, link 12A, and gears 8A and10A, having the respective above-named properties of 6, 12, 8, and 10,and having: engagement of 6 and 8, and of 8 and 10, engagement of 6A and8A, and of 8A and 10A, the pedal crank being coupled to 12, the annulargear 6 being coupled to the drive sprocket of the transmission, gear 10being coupled to gear 10A, the annular gear 6A being coupled to thesuspension arm, link 12A being fixed to the frame.
 3. A bicycle having aframe, at least a rear wheel coupled to the frame via a movablerear-suspension arm, and a drive and suspension system including:multiple main sprockets, with a derailleur to shift between the drivesprockets and a chain linking a drive sprocket to a sprocket coupled tothe rear axle, rotating about the axis of rotation of the main sprocket(hereafter called the “main axis”), an annular gear 6 whose teeth pointinward toward the main axis, a gear 10 rotating about the main axis, alink 12 pivoting at one end about the main axis, a gear 8 rotating aboutanother pivot attached to link 12 at its other end, a movable suspensionarm pivoting about the main axis.
 4. The bicycle of claim 3, furtherincluding annular gear 6A, link 12A, and gears 8A and 10A, having therespective above-named properties of 6, 12, 8, and 10, and having:engagement of 6 and 8, and of 8 and 10, engagement of 6A and 8A, and of8A and 10A, the pedal crank being coupled to 12, the annular gear 6being coupled to the drive sprocket of the transmission, gear 10 beingcoupled to gear 10A, the annular gear 6A being coupled to the suspensionarm, link 12A being fixed to the frame.